This invention concerns an hydraulically operated valve control system for an internal combustion engine. It also concerns an internal combustion engine equipped with such a system.
Internal combustion engines are more and more equipped with multi-valve injection systems where two inlet valves and/or two exhaust valves are provided for each cylinder in order to optimize the flow of the air-fuel mixture or the exhaust gases to or from a combustion chamber. These sets of two valves must be driven in such a manner that the valves have parallel movements, that is the same lift and speed for both valves.
EP-A-O 736671 teaches the use of balancing springs which engage a piston fast with each valve in order to move each valve towards a closing position. Such an approach works if the friction forces for each valve and the rigidity of the two springs are identical and if the hydraulic feeding circuits are symmetrical. Such conditions cannot be guaranteed because of the tolerances in the fabrication of the valves, in the fabrication of the springs and in the distribution of the fluids circuits within a cylinder head. Therefore, it is not sure the two valves of the prior art actually have the same movements.
U.S. Pat. No. 5,619,965 discloses an arrangement for balancing valves in a hydraulic camless valve train. Valve position sensors are used in conjunction with an electronic control unit to pilot opening and closing of solenoid valves. Such an arrangement is complex and expensive since it requires sensors and solenoid valves dedicated to each inlet valve/exhaust valve of the engine.
It is desirable to provide an hydraulically operated valve control system which efficiently controls the movements of two valves, without requiring electronic sensors or other complex and expensive equipments.
An aspect of the invention concerns an hydraulic operated valve control system for an internal combustion engine having at least one cylinder provided with two valves driven with oil coming from a source of oil under pressure, each valve being controlled by an hydraulic actuator fed with oil under pressure through a respective feeding line. This system is characterized in that it includes an hydraulic flow divider comprising an hydraulic valve adapted to distribute the flow of oil coming either, from said source or from said two feeding lines between said two feeding lines, depending on the ratio of oil flow-rates in these two lines.
Thanks to an aspect of the invention, the hydraulic valve can evenly distribute oil to the two inlet valves or two exhaust valves when these valves are supposed to be lifted.
Similarly, when the valves are supposed to be closed, the flow divider of the system of the invention accommodates evenly the two flows coming from the two inlet or exhaust valves.
According to further aspects of the invention, the control system might incorporate one or several of the following features:                The hydraulic valve comprises a valve member which is movable depending on pressure drops created across two throttles located respectively in a connecting line between said source and one of the feeding lines.        The valve member is automatically moved towards a position of balance of the pressure drops across these throttles.        The valve member is advantageously movable in a valve body which is defines a bore, where the valve member is slidably movable and which forms an internal volumes where oil under pressure acts on the valve member in order to move it in translation along a longitudinal axis, these volumes being fluidically connected to the connecting lines either upstream or downstream of the throttles.        The hydraulic valve body defines four internal volumes, two internal volumes being fluidically connected to a first connecting line in fluid connection with a first valve, respectively upstream and downstream of a first throttle located in this first connecting line, whereas the other two internal volumes are fluidically connected to a second connecting line in fluid connection a second valve, respectively upstream and downstream of a second throttle located in the second connecting line.        The pressure within the internal volume connected to the first connecting line upstream of the first throttle and the pressure within the internal volume connected to the second connecting line downstream of the second volume tend to move the valve member in a first direction along the longitudinal axis of the bore, whereas the pressure within the internal volume connected to the first connecting line downstream of the first throttle and the pressure within the internal volume connected to the second connecting line upstream of the second throttle tend to move the valve member in a second direction opposite the first direction.        According to a first embodiment of the invention, the throttles are each provided on a shuttle movable between two positions, depending on the direction of oil flow in the feeding lines. In such a case, the internal volumes of the hydraulic valve body are advantageously connected to the feeding lines upstream or downstream of the corresponding throttle, irrespective the position of the shuttles.        According to another embodiment of the invention, the throttles are provided on fixed part of the connecting lines, check valves being respectively provided between the internal volumes of the hydraulic valve body and the throttles.        The flow divider also includes two solenoid valves connecting selectively the hydraulic valves respectively to the source of oil under pressure and to a low pressure circuit.        
An aspect of the invention also concerns an internal combustion engine provided with a control system as mentioned here above.